The present invention concerns a substrate with a deposited organic diffusion barrier layer. The invention also concerns a process for production of a substrate with a diffusion barrier layer and uses thereof.
The storage of foodstuffs, drugs, delicate materials and micro-electronic components for a lengthy period taking into account ambient influences is a vital problem of our time. New materials and processes to protect the stored materials against permeation of damaging gases and vapours, e.g. oxygen and water vapour, must be used in order to protect the stored materials. Plastic films as a highly functional packaging medium are already used in many places as a substitute for metal and glass elements. Taking into account environmental protection aspects, chemically inert and transparent films of polyethylene terephthalate (PET), polypropylene (PP) or polyethylene (PE) and plastic films with similar action are used to a great extent. If these films are damaged for example by heat, no toxic vapours occur. The properties of conventional PET, PP or PE films are not, however, such that they can adequately protect delicate materials as described above. For this reason in the known manner laminate structures of several layers of polymers, for example ethyl vinyl alcohol (EVOH), are used in order to compensate for the relatively low barrier properties of the individual coatings against gases.
Also, according to known processes plastic films are coated with thin diffusion blocking or barrier layers which consist of metal or metal oxides. These coatings must be thin, elastic and free from pores (pinholes) or hairline cracks (microcracks) and must not lose their permeation properties even over a long storage period.
Metal oxide barrier layers are optically transparent, microwave-compatible, and fulfil the ecological requirements, but because of their rigidity their area of application is rather limited. Plasma-polymerised coatings with compounds containing fluorine or sulphur allow the reduction of solvent permeation in plastic containers. Also, multilayer systems have been developed consisting of oxide-like barrier layers embedded in polymer-like materials.
Thin hydrocarbon barrier coatings have proved good alternatives to stiff, brittle metal oxide barrier layers, as described for example in WO,A1 96/28587 and EP,A1 0739655. These thin hydrocarbon coatings are preferably produced by means of DC magnetron discharge processes, high frequency or microwave discharge.
DE,A1 4316349 also describes the production of diffusion barrier layers in hollow bodies, where this is achieved by means of a microwave process.
The two European patent specifications EP,B1 0381110 and 0381111 propose the production of a protective coating for electroactive passivate coating of semi-conductor elements generated by means of a high frequency low pressure plasma deposition of gaseous hydrocarbons.
U.S. Pat. No. 5,041,303 describes the production of inorganic and diamond-like diffusion barrier layers which are produced by means of electromagnetic energy in the microwave frequency range. Finally EP,B1 0575299 describes the production of a barrier film by means of high frequency plasma process, where the barrier layer is deposited in a vacuum chamber from a plasma generated from non-saturated hydrocarbons, amongst others.
EP-A1 0176636 discloses a thin polymerised film of high density, high hardness and high strength. This layer is deposited on the surface of a substrate by plasma polymerisation. The gas used to generate the plasma contains a halogenated alkane and/or an alkane with either hydrogen and/or a halogen. The atomic ratio halogen/hydrogen in the gas lies in the range of 0.1:1 to 5:1. The plasma temperature lies in the reaction zone range at 6000xc2x0 K. or higher but below 30,000xc2x0 K. The pressure during polymerisation is 0.001 to 1 Torr. The thin polymer layer is used as a protective coating for numerous objects, also as a harder surface, rust protection coating, scratch protection, gas barrier etc. The protective coating is particularly suitable as a protective film for magnetic data carriers.
In particular, in the area of application described above, storage of commodities, for example delicate drugs or similar, it is important that the permeation of oxygen and other gases is low or almost zero and this impermeability remains guaranteed even at high ambient humidity. It is quite possible, using the metal oxide coatings described in the state of the art, to generate a high oxygen barrier effect but usually this diminishes greatly, i.e. the oxygen permeation increases, as the ambient or relative humidity rises. In particular, in tropical zones this trend constitutes a major problem which can lead to premature degradation of foodstuffs and drugs.
The task of the present invention is to create a substrate with an improved diffusion barrier layer which has better barrier properties against oxygen and other gases, in particular at high ambient humidity.
According to the invention the task is solved with regard to a substrate with a diffusion barrier based on carbon and hydrogen at a content of 20-80 at % of both elements, whereby the barrier effect of the diffusion barrier layer is sustained even in damp air.
Preferably, in the diffusion barrier layer at least one element of the group according to the paragraph above has a content of 0.1-3 at %.
The diffusion barrier layer is constructed on the basis of carbon and hydrogen, preferably with a content of 20-80 at % but in particular 30-70 at %.
The diffusion barrier layer as stated is preferably largely a hydrocarbon plasma polymer with non-polar basic structure, i.e. the diffusion barrier layer is produced by plasma polymerisation of at least one hydrocarbon monomer, preferably with maximum 8 C-atoms, with inert gases mixed in. The diffusion barrier layer can be produced by means of the plasma of a magnetron sputtering source or by combination of the sputtering source with the plasma-induced gas phase polymerisation. Alternatively, the barrier layer can be produced by means of inductively coupled microwave discharge.
When DC magnetron sputtering plasma is used, it has proved advantageous to overlay this with a plasma-induced gas phase polymerisation and apply an LF/HF (10 kHz-100 MHz) induced negative bias potential to the substrate.
In the case of a microwave discharge, it has proved advantageous for the hydrocarbon gas-inert gas mixture to be processed with a surplus of hydrocarbon gas. The inert gas can be helium, neon, argon or other inert gases as pure gases, but according to a preferred embodiment advantageously a mixture of argon and helium is used.
When a magnetron sputtering source is used, preferably a hydrocarbon-inert gas mixture is used, the latter in particular in the form of helium, neon and/or argon.
With reference to the plasma polymerisation for production of a substrate with diffusion barrier layer, the task is solved according to the invention in that the barrier layer is produced by means of at least one pulsed or continuous DC magnetron sputtering source plasma or by means of inductively coupled pulsed or continuous microwave discharge.
Preferably, the reactor is first evacuated to a pressure below 5.10xe2x88x923 mbar, preferably below 1.10xe2x88x924 mbar, then the reaction gases added until a value not above 1 bar, preferably not above 10 mbar, is reached and maintained. The power of the energy source with a sample diameter of around 12 cm is suitably 50-1000 W, in particular maximum around 500 W.
For the process according to the invention a wide range of reactive gas components can be used in particular an alkane, alkene or alkyne and/or mixtures thereof, also with at least one inert gas as carrier gas. The inert gas used in plasma polymerisation is for example helium, neon, argon or mixtures thereof. In the case of a pulsed DC magnetron sputtering source preferably helium is used, in the case of an inductively coupled microwave discharge, a mixture of argon and helium.
All reactive gas components are suitably used as pure hydrocarbon gases. In particular methane, ethane, propane or unsaturated hydrocarbons of ethane, propane, butane but also alkynes, separately or mixed with other components.
The use of diffusion barrier layers according to the invention is as stated extremely wide. Preferred applications concern the coating of polymer materials such as in particular flexible polymer films. These diffusion barrier layers are extraordinarily effective protective coatings against gases, water vapour, aromatics, organic and inorganic volatile compounds and liquids in particular against watery liquids. The coated polymer films consist for example of polypropylene, polyethylene, polyamide, amended sheet polyethylene terephthalate etc. Laminate films of the said polymers and objects formed, blown or deep-drawn from the films, such as in particular containers, are covered by the term polymer films.
A further use of a substrate with diffusion barrier layer according to the invention lies in packing materials, in particular for sterilisation or pasteurisation of a product arranged in the packing. Here containers in direct contact with the foodstuff are extraordinarily important for the inner and outer coating. Naturally moist foodstuffs are particularly delicate, the diffusion barrier layers according to the invention are particularly suitable for use in damp environments. Packing materials consist of polymers, for example polypropylene PP, polyethylene PE, polyamide PA, PET, and laminate films made from various polymer materials, e.g. PP/PE, PET/PP, PET/PE, PE/PA. Such packing materials, e.g. foils, can be fitted i.e. coated or laminated with barrier layers according to the invention. Because of the good flexibility or mechanical properties of the diffusion barrier layers applied, foils coated in this way can easily be rolled and unrolled. Also, such packing materials are particularly suitable for foodstuffs as no organoleptic or chemical changes to the filling according to the Foodstuffs Law can occur. The said migration protection and perm-selectivity is particularly important for the packing of foodstuffs as foodstuffs are often packed under inert gas (CO2, N2 or mixtures thereof). The higher permeability of CO2 in comparison with oxygen consequently gives additional protection to the filling. Thus, the barrier layer is often required to provide a high oxygen and water vapour barrier.
Further advantageous possible applications are listed merely in brief:
UV protection
medical engineering, protective coatings for implants, in particular in moist environments, sterilisation and as protective coatings for treatment instruments, sterilisation
protective coatings for ceramic material and glass-like objects, carbon and glass fibres and/or composite materials thereof, against volatile and non-volatile compounds, in particular chemicals
protective coatings for polymer strips and tapes
protective coatings for recycled products.
As well as the broad application spectrum another substantial advantage of the diffusion barrier layers according to the invention lies in their sterilisability or pasteurisability. The following known processes can be used in order to sterilise or pasteurise products (films, containers, coated materials) equipped with diffusion barrier layers proposed according to the invention:
sterilisation with water vapour and water in autoclaves up to 150xc2x0 C., in particular up to 135xc2x0 C.; no mechanical damage and no subsequent discoloration of the coating
sterilisation with gases (ethylene oxide, H2O2 etc), no chemisorption or adsorption of gases on the chemically inert barrier layer
high pressure sterilisation
gamma sterilisation
high pressure, gamma and plasma sterilisation
pasteurisation at 70-100xc2x0 C.